1. Field of the Invention
This invention relates generally to resistive gas sensors, and is more particularly concerned with a method for the use of sensor arrays comprising such sensors.
2. Discussion of the Prior Art
A resistive gas sensor, as is well known, comprises, in general terms, a semiconducting sensing element such that its electrical resistance changes in response to a change in the concentration of at least one gas or vapor (sometimes referred to as a "target gas") that is present, to a substantially greater extent than to other gases or vapors.
The sensor is thus selective in favor of the target gas and is accordingly used for detection, and, where required, measurement, of the target gas. Such a sensor will be referred to as a sensor of the kind specified.
Semiconducting oxide materials, when used for gas sensors, provide devices which are inexpensive, light and robust. However, they suffer a reputation for unacceptable cross-sensitivity to different gases, particularly to water vapor, which is always present in the atmosphere at concentrations which can vary widely. Devices based on tin dioxide, such as are widely use, show strong effects of changes in relative humidity, both on the baseline resistance and on the sensitivity of the resistance change to the presence of gases such as carbon monoxide.
These devices also have a reputation for excessive baseline drift and show a long stabilization time in the atmosphere after the temperature of the device has first been raised to its operating value.